1. Field of the Invention
The present invention relates to a power control apparatus for controlling power for a system including a plurality of printing apparatuses and a method of controlling the same.
2. Description of the Related Art
Many recent printing apparatuses are provided with a reducing power consumption function, which is called an energy saving mode or a sleep mode. For example, a printing apparatus incorporates a timer. When the user access interval to the printing apparatus exceeds a predetermined time, power to the printing apparatus is partially or wholly shut down using the internal timer. Power consumption reduction is thus implemented. Several power saving levels are configured for the energy saving mode. As the power saving level becomes higher, the printing apparatus shifts to an energy saving mode for larger power consumption reduction.
According to the related art, the higher the power saving level is, the longer the time to return to a printable state is. Hence, a general trend indicates that as the energy saving level rises, the convenience (servability) for the user becomes poorer. In a printing system formed by connecting a plurality of printing apparatuses to a network, the printing apparatuses independently receive access generated by the host at random. For this reason, the control mechanism of the energy saving mode cannot effectively function in such a system.
To cope with this problem, Japanese Patent Laid-Open No. 2000-322161 proposes a power control method that defines the relationship between the power load of an entire network and a service capability representing servability as a numerical value. These values are compared to set such a power consumption that implements servability close to the service capability and more than the capability. This power control method makes it possible to reduce power consumption to provide a service more than the currently necessary service capability. At the same time, the necessary servability can be ensured without causing deterioration of the servability.
The power control method of Japanese Patent Laid-Open No. 2000-322161 can control to make power consumption approach the minimum value necessary for implementing the service. However, it is difficult to control the power consumption to a given target power consumption or less. Additionally, control is cumbersome because the load of the entire network needs to be measured periodically.